Inside Unmanned Systems

AUG-SEP 2018

Inside Unmanned Systems provides actionable business intelligence to decision-makers and influencers operating within the global UAS community. Features include analysis of key technologies, policy/regulatory developments and new product design.

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74 unmanned systems
inside
August/September 2018
MARINE INNOVATION
ber of designs for unmanned aircraft
that could also travel underwater, f ly-
ing either through rotors, fixed wings
or f lapping wings.
However, "traveling underwater is
difficult, because motors are at their
peak efficiency in a relatively narrow
range of rotation speeds," Bousquet
said. "Air-water vehicles with propel-
lers have their propellers spin very
fast in air and very slow underwater.
Accordingly, they are probably very
inefficient underwater." In contrast,
he said, UNAv is designed for both ef-
ficiency and long-range travel.
PROTOTYPE TESTED
The researchers built a prototype to
test their design's critical maneuver—
transitioning between f lying in the air
and dipping its keel down to sail in
the water. Accomplishing this move
does not necessarily require a sail, so
Bousquet and his colleagues Michael
Triantafyllou and Jean-Jacques Slotine
decided not to include a sail in their
prototype to simplify their preliminary
experiments.
The scientists tested their prototype
on the Charles River. They equipped it
with auto-pilot instrumentation, GPS,
inertial measurement sensors and ul-
trasound to help control the craft and
track its height above the water.
Because the prototy pe lacked a
sail or any other mechanism to get it
moving, the researchers hung it from
a fishing rod attached to a boat and
towed the robot down the river. "The
towing line generates a force ver y
similar to that of a sail, hence it can
be thought of as a simulated sail,"
Bousquet said.
The researchers used a lightweight
off-the-shelf competition glider air-
frame so it could f ly at relatively low
speeds. "The f lip side of being opti-
mized for lightweightness was that
the airframe was not very robust, so
we could not afford many crashes and
everything had to work just right from
the start," Bousquet recalled. "This
made testing quite stressful."
All in all, when the prototype reached
a speed of about 20 miles per hour, the
robot autonomously f lew, successfully
riding the wind on its own. A remote
microcomputer could then send the
robot orders to dip low enough to sub-
merge its keel in the river, steer away
from the tow boat, and then fly back up,
lifting its keel out of the water.
FUTURE DESIGNS
Bousquet envisions the UNAv will have
auxiliary solar cells on its wings and a
foldable propeller driven by solar power.
"Every now and then—say, 5 percent of
the time—we envision that the UNAv
will use its solar-charged propeller to
zoom to higher altitudes to gather data
of interest," he said.
He also noted this design is geared
toward small vehicles. "It w ill not
work for airliner-sized systems," he
said. "Larger systems have a heavi-
er mass per amount of w ing area,
so they require more w ind to stay
aloft." Still, "at the upper end of pos-
sible weight and sizes, a recreational
one-seater 'f lying sailboat' is physi-
cally plausible, which would be really
cool," he noted.
Traykovski, who investigates how
storms interact with coasts, envi-
sions one day dropping a few of these
robots into hurricanes. "Right now
NOA A [the National Oceanic and
Atmospheric Administration] moni-
tors hurricanes with hurricane hunter
airplanes, which carry out overf lights
to drop a few instruments into the
storms to measure their pressure and
other properties at a given time," he
said. "With robotic albatrosses, you
can imagine them staying with a hur-
ricane as it goes up the coast for weeks
at a time."
Future research not only needs to
test how UNAv performs with a sail
added to it, but to explore how well it
performs against waves. Still, with low
winds, waves are relatively small, "so
touching the water is a manageable
challenge," Bousquet said. In contrast,
with high winds and waves, "there is
enough wind to be f lying like an alba-
tross, and no need to dip the keel in the
water, so in principle, the waves are
less of a problem."
To help UNAv deal with any large
waves that it cannot avoid, there is
technolog y "for drones to autono-
mously navigate through forests us-
ing machine-vision and path-plan-
ning algorithms," Bousquet noted.
"We want to use these technologies to
teach the UNAv how to f ly in strong
weather with large waves."
Future research should explore what
the UNAv should do in case of a crash.
Bousquet noted there are prototypes of
small UAS that are able to crash land
A previous study found
the albatross spends
more energy when it's
walking around its nest
than when it's flying
thousands of kilometers
in the wind."
Peter Traykovski, associate scientist, Woods Hole
Oceanographic Institution
"